Draft gears for rail cars typically include a housing with a series of elastomeric spring assemblies or units arranged within the housing. The spring assemblies are arranged in stacked relation relative to each other to absorb shocks during coupling and other impacts between adjacent rail cars. The use and design selection of any particular spring unit is dependent upon the energy to be absorbed and the intended application of the spring.
Each elastomeric spring assembly typically includes an annular elastomeric spring member which is sandwiched between and joined to two metal plates. Each metal plate normally includes a surface incongruity which is intended to capture a portion of the elastomeric spring member that is forced into the incongruity during a cold-forming process, i.e., the direct application of pressure which causes the spring member elastomer to flow into the incongruities, thereby joining or bonding the plates to the spring member. The plates of a typical spring assembly typically include a profile about the periphery thereof. The plate profile is complementary to a design provided on the interior of the draft gear housing to promote sliding movement of the spring units within the draft gear housing thereby enabling the stacked spring units to combine in operation to absorb the very substantial impact loads applied to the rail cars during their movement and, more significantly, when the cars are being coupled into train consists.
With the spring assembly illustrated for purposes of this disclosure, it is imperative that the annular elastomeric spring member is properly and accurately located relative to the plates during assembly of the spring assembly. In the illustrated spring assembly, it is important that the elastomeric spring member is centered or arranged concentrically relative to the plates joined to opposite sides thereof.
As will be appreciated by those skilled in the art, when the elastomeric spring member is offset or not properly centered relative to the plates, the very substantial impact loads applied against the spring assembly, following its insertion into a draft gear housing, will cause unequal load distributions across opposing faces of the spring assembly. The uneven load distribution detracts from the effectiveness of the individual spring assemblies and thereby detracts from the ability of the draft gear to operate properly in absorbing the shock loading of the rail cars.
Besides those problems inherent with uneven load distribution, when the elastomeric spring member is not accurately located, the plates of the spring assembly have been known to shift from their normal parallel relationship and tend to diverge in relation to each other under the high loading applied thereto during operation of the draft gear. The divergence of the plates from their normal parallel relationship relative to each other causes the elastomeric spring member to be squeezed or pinched on one side of the spring assembly. Under the extremely high impact forces which are applied to the spring assembly during operation of the draft gear, this pinching or squeezing of the elastomeric spring often causes the elastomer of the spring member to extend beyond the periphery of the plates and scrape against the draft gear housing. As will be appreciated, this faulty condition requires repair and/or replacement of the elastomeric spring assembly and can further result in the need to repair or replace the draft gear housing.
Fabrication of an elastomeric spring assembly involves a labor intensive process. One well-known method of forming the spring assembly involves the use of a press capable of developing the high pressure necessary to effect the cold-formed interlock between the elastomeric spring member and the plates. During this process, one plate of the spring assembly is typically held in a first fixture while the second plate is typically held in a second fixture spaced from the first fixture. The annular elastomeric spring member is placed between the plates and the press is operated to apply the force necessary to effect a cold-formed interlock between the plates and the elastomer member and to provide a permanent compression set to the spring assembly or unit.
Various attempts have been proposed for properly and accurately arranging or locating the annular elastomeric spring member relative to the plates prior to the plates being compressed into relation with the spring member by the press. One attempt involves the press operator attempting to visually lay or locate the spring member in proper relation relative to the plates. This attempt has failed primarily due to human error. When the spring assembly is inaccurately assembled due to improper locating of the spring member relative to the plates, further labor efforts are required to disassemble the spring assembly. Because of the preset involved in the compression procedure, the spring member often cannot be readily reused. Thus, not only is there a loss of the labor costs incurred with improper fabrication of the spring assembly but material costs likewise increase from inaccurately manufactured spring assemblies.
An alternative proposal for fabricating the spring assembly involves using specifically sized annular locating rings for locating the elastomeric spring member relative to the plates of the spring assembly. Prior to the press being operated to compress the spring member and the plates into a spring assembly, the locating ring is snugly fit over the elastomeric spring member. After the locating ring and spring member are properly positioned relative to the plates, the locating ring is removed from about and over the spring member and the press is operated to form the spring assembly.
Serious drawbacks are associated with this later proposal. First, when the locating ring is removed, the annular spring member is often inadvertently displaced in view of the forces acting to remove the ring therefrom. Thus, the spring member is not properly centered and the labor intensive effort involved with centering the spring member is lost. Because the operator is normally unaware of the shifting of the annular spring member from its proper location, the press is operated and a faulty or non-acceptable spring assembly results. Second, if improper positioning of the spring member is noticed, the operator needs to duplicate the effort and time including replacing the locating ring over the spring member to effect proper relocation of the spring member relative to the plates. Of course, the need to carefully separate the locating ring from the annular spring member (especially in those duplicative positioning situations) increases the labor intensive aspects of the spring assembly manufacturing process.
When the spring members are initially received at a press station they normally have a preformed annular configuration. As the spring members are retained in inventory, they have a tendency to change size. That is, both moisture and heat tend to alter the size of the preformed annular spring member. Depending on how long the preformed annular spring members have been held in inventory, different sized locating rings are required to fit over the various sizes of the annular spring member. Of course, if any of the locating rings are lost or misplaced, production of the elastomeric spring assembly can be adversely affected.
The use of specifically sized locating rings to accurately position the annular spring member relative to the plates of the spring assembly furthermore complicates the vertical spacing necessitated between the press fixtures which retain the plates in the press. Since the locating ring must be removed from about the elastomer spring member prior to operation of the press, there will be an attendant increase in the vertical space required to remove the locating ring from around and over the annular spring member without effecting inadvertent displacement of the annular spring member. Thus, the use of locating rings furthermore increases the necessary spacing requirement between the press fixtures and thereby reduces the number of tiers of spring assembly forming stations which can be incorporated into a single press.
Thus, there is a need and a desire for an improved method for making elastomeric spring assemblies. The need for an improved method likewise lends itself to a need and a desire for an improved apparatus capable of effecting an improved method of forming the elastomeric spring assembly.